It is common for the modern intake manifold for an internal combustion engine to be formed from a variety of materials, including both metal and polymeric material. Both internal and external bracing (formed on the surface of the manifold) is often desired to provide a reduction of noise radiating from the manifold's surface (reduced NVH) and to provide strength and thereby allow for increased pressure while preventing manifold failure under a backfire condition. Without such posts, the manifold would only comprise a large, unsupported panel which would have the propensity to resonate and to cause undesired noise. Unsupported manifolds also are prone to damage under the above-mentioned backfire condition.
The internal bracing is typically provided in the form of posts formed from either the same material or a different material from the manifold's parent material. In high performance engine applications, the size of the post in the intake manifold can have a negative impact on engine performance. The size of these posts is normally dictated by the weld bead width and the interface between the upper and lower shells as well as by draft requirements on the post and post stability for welding.
The size of the posts often presents a challenge to airflow efficiency. If a larger post is used the result may be that the cross-sectional area of the post reduces the flow area within the intake manifold to an unacceptable degree. This reduction in flow area may result in limiting the peak power of the engine. This issue is particularly important for the naturally aspirated engine, including engines without pressure charging on the intake of the type provided by superchargers or turbochargers.
Experience has shown that the size of the intake manifold may be increased to compensate for the reduction in flow area due to the posts. However, a larger manifold increases both product cost and weight while also complicating packaging. The larger manifold may also demand either an increase in the number of the posts or an increase in the diameter of the posts, with either outcome potentially compromising the purpose of providing the posts in the first place.
In an effort to reduce the diameter of the posts the size of the weld bead was reduced. While post diameter was reduced burst strength was also reduced. Thus a reduction of the size of the weld bead was found not to be an answer to the problem.
As a further development in intake manifold posts thread forming screws without weld beads have been employed that provided a reduction of post diameter from 30 mm to 14 mm (more than 50%). However, in this construction the screw does not offer any sealing function and presents a potential leak path to atmosphere. In response a dust cap has been used in the past to cover the head of the screw with RTV sealant applied between the screw head and the interior of the cap. However, while providing sealing to a certain extent this approach failed to provide an ideal solution in a production environment.
Thus known solutions are either impractical for production applications or are less than ideal insofar as they result in little if any reduction in the size of the post or provide inadequate burst strength. Accordingly, a post for use within an intake manifold that demonstrates good air flow, reduced NVH and adequate burst strength remains wanting.